Microelectromechanical device with integrated conductive shield

ABSTRACT

A microelectromechanical device and method of fabricating the same, including a layer of patterned and deposited metal or mechanical-quality, doped polysilicon inserted between the appropriate device element layers, which provides a conductive layer to prevent the microelectromechanical device&#39;s output from drifting. The conductive layer may encapsulate of the device&#39;s sensing or active elements, or may selectively cover only certain of the device&#39;s elements. Further, coupling the metal or mechanical-quality, doped polysilicon to the same voltage source as the device&#39;s substrate contact may place the conductive layer at the voltage of the substrate, which may function as a Faraday shield, attracting undesired, migrating ions from interfering with the output of the device.

FIELD

[0001] The present invention is related to integratedmicroelectromechanical devices and more particularly, to semiconductormicroelectromechanical devices with an integrated conductive shield, anda method for manufacturing the same.

BACKGROUND

[0002] Microelectromechanical devices are useful in many applications.These devices range from automobile sensors to actuators used on spaceexploration vehicles. Generally, these sensors and actuators provideinformation about environmental conditions, and/or react to changes inthe environmental conditions. For instance, amicroelectromechanical-pressure-sensor device may be used to measure anautomobile's engine manifold pressure (or vacuum). In operation, themicroelectromechanical-pressure-sensor device provides an electricaloutput that is proportional to the manifold pressure (or vacuum). Thiselectrical output may be used by an engine management system forcontrolling fuel delivery to the automobile's engine.

[0003] In another useful application, one or moremicroelectromechanical-accelerometer devices may be employed formeasuring the acceleration or, conversely, the deceleration of avehicle. In crash situations, these devices may enable a crash detectionsystem to determine whether to deploy an airbag.

[0004] Additionally, microelectromechanical devices are pervasivelydeployed in many types of industrial equipment. From simplesingle-fixture assembly machines to high-volume complex machinery, thesemicroelectromechanical devices supply feedback for process and qualitycontrol.

[0005] Microelectromechanical devices may be incorporated as componentsin many medical equipment devices, such as respiration devices, dialysismachines, and infusion pumps. In surgical procedures, physicians areaided by data from various pieces of surgical equipment that employmicroelectromechanical devices. These devices generally furnishinformation about the surrounding area in which the surgeon isoperating. For example, the gage or absolute pressure of the area inwhich a catheter is positioned may be provided by an electrical outputof a microelectromechanical-sensor device installed on the tip of thecatheter. During an operation or other medical procedure, thiselectrical output may provide valuable feedback to the surgeon.

[0006] These cited examples indicate the breadth ofmicroelectromechanical devices used in various applications in today'sautomated world, however many other microelectromechanical devicesexist. Moreover, the types of devices, and their related applicationscontinue to proliferate. Due to the widespread adoption and theever-decreasing size of microelectromechanical devices, maintaining orimproving the quality and performance of these devices may requireimplementing device and process control improvements so that the devicesperform accurately, reliably, reproducibly, and repeatedly.

[0007] Environmental conditions acting on or impressed uponenvironmentally susceptible microelectromechanical devices may causeunwanted effects that may prevent the devices from attaining acceptableperformance levels. These environmental conditions, which often containenergy in one form or another, may cause undesired effects, such asdrift or instability, in the device's electrical output. To reduce oreliminate the drift or instability, a system and method that minimizesor eliminates the undesirable exchange of energy would be desirable.

SUMMARY

[0008] According to one embodiment, a semiconductormicroelectromechanical device, such as a pressure sensor oraccelerometer, may include a substrate over which a sensing element isformed. A conductive shield may be fabricated over at least a portion ofthe sensing element. Further, the conductive shield may be coupled witha substrate. By this coupling, the conductive shield and substrate mayform an encapsulation of at least a portion of the sensing element.Moreover, coupling the conductive shield with the substrate may allowplacing both the conductive shield and substrate at substantially thesame voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Exemplary embodiments are described below in conjunction with theappended figures, wherein like reference numerals refer to like elementsin the various figures, and wherein:

[0010]FIG. 1 is a conceptual diagram illustrating a side cross-sectionof a microelectromechanical device's substructure at a first phase ofprocessing;

[0011]FIG. 2 is a conceptual diagram illustrating a side cross-sectionof a microelectromechanical device's substructure at a second phase ofprocessing;

[0012]FIG. 3 is a conceptual diagram illustrating a side cross-sectionof a microelectromechanical device's substructure at a third phase ofprocessing;

[0013]FIG. 4 is a conceptual diagram illustrating a side cross-sectionof an exemplary embodiment of a semiconductor microelectromechanicaldevice with integrated conductive shield at a fourth phase ofprocessing;

[0014]FIG. 5 is a conceptual diagram illustrating a side cross-sectionof an exemplary embodiment of a semiconductor microelectromechanicaldevice with integrated conductive shield at a fifth phase of processing;

[0015]FIG. 6 is a conceptual flow diagram illustrating an exemplaryembodiment of the method of fabricating a semiconductormicroelectromechanical device with integrated conductive shield; and

[0016]FIG. 7 is a conceptual flow diagram illustrating another exemplaryembodiment of the method of fabricating a semiconductormicroelectromechanical device with integrated conductive shield.

DETAILED DESCRIPTION

[0017] The embodiments of the microelectromechanical device describedherein are described in relation to a preferred microelectromechanicalpressure sensor and its architectural components. The describedarchitecture and processes for fabricating the microelectromechanicalpressure sensor are likewise applicable to other microelectromechanicaldevices.

[0018]FIG. 1 is a conceptual drawing illustrating an embodiment of across-section of the substructure of a microelectromechanical device 100at a first processing phase. While FIG. 1 and other subsequent figuresillustrate the microelectromechanical device's substructure at certainprocessing phases, these phases are for illustration purposes only andnot necessarily intended to limit the scope of the present embodiments,provide sequential processing steps, or provide an inflexiblefabrication recipe.

[0019] Referring to FIG. 1, the microelectromechanical device 100includes a substrate 102, a layer-of-substrate silicon 102 a, aburied-oxide layer 104, and a top-epitaxial layer 106 deposited atop thelayer-of-substrate silicon 102 a.

[0020] The substrate 102 may include non-semiconductor substratematerial, such as sapphire or ceramic, and/or may include semiconductorsubstrate material, such as an N-type or a P-type silicon wafer.Preferably, the substrate 102 is a bulk silicon substrate. Siliconenables the use of many common silicon semiconductor-processingtechniques, such as masks, implants, etchings, dopings, and others. Inthe preferred microelectromechanical pressure sensor, the substrate 102devices may be fabricated from a heavily P-type doped silicon wafer.

[0021] The substrate 102 may exist in the final microelectromechanicaldevice or may be removed during processing. For instance, in fabricatingthe preferred microelectromechanical pressure sensor, the “backside” ofthe substrate 102 may be etched away to form a silicon diaphragm forsensing pressure. Accordingly, the substrate 102 may contain one or moreopenings for forming and for providing access to the diaphragm. In otherembodiments, the substrate 102 may contain openings for suspendingmoveable elements of the microelectromechanical device. To create theseopenings, portions of the substrate 102 may be etched using chemicaletching processes.

[0022] Implanted in the substrate 102 is the buried-oxide layer 104.Preferably, this buried-oxide layer 104 is created in the substrate 102using a Separation by IMplantation of OXygen (SIMOX) process.Alternatively, the buried-oxide layer 104 may be formed using a BondedSilicon On Insulator (BSOI), Bonded and Etchback Silicon On Insulator(BESOI), or other similar process. Other processes for creating theburied-oxide layer 104 are possible as well. During the SIMOX process,oxygen ions are implanted into one or more surfaces of a bulk-siliconsubstrate using an ion-implantation process. Preferably, the oxygen ionsare implanted through only one surface, such as substrate surface 103.By controlling the ion-implanting process, the oxygen atoms that areimplanted into the substrate 102 via the substrate surface 103 createthe buried-oxide layer 104 at a predetermined depth below the surface ofthe substrate.

[0023] Creating the buried-oxide layer 104 beneath the substrate surface103 results in a layer-of-substrate silicon 102 a resting aboveburied-oxide layer 104. This layer-of-substrate silicon 102 a comprisesa layer of bulk substrate that is isolated from the remaining bulksubstrate by the buried-oxide layer 104. In a preferred embodiment, thelayer-of-substrate silicon 102 a and the substrate 102 “sandwich” theburied-oxide layer 104. This layer-of-substrate silicon 102 a provides abase upon which other layers of the microelectromechanical deviceelements may be formed.

[0024] The SIMOX process may also include a high-temperature annealprocess during and after creating the buried-oxide layer 104 tofacilitate enhanced control over the ion-implant process, and tominimize defects in the substrate surface. After the high-temperatureanneal, the unit cells of the substrate are preferably arranged in asingle-crystal silicon structure. This single crystalline structureprovides a surface upon which a single-crystal epitaxial silicon layermay be deposited.

[0025] Using standard epitaxial techniques and processes, thetop-epitaxial layer 106 may be deposited over the substrate 102. In anexemplary configuration, the top-epitaxial layer 106 is deposited overthe layer-of-substrate silicon 102 a. The standard epitaxial techniquesand processes for depositing the epitaxial layer 106 include chemicalvapor deposition (CVD), atmospheric pressure chemical vapor deposition(APCVD), low-pressure chemical vapor deposition (LPCVD), plasma enhancedchemical vapor deposition (PECVD), and other deposition techniques.

[0026] Further, dopant materials may be introduced during the depositionprocess, which may cause the top-epitaxial layer 106 to becomeelectrically conductive. Alternatively, the top-epitaxial layer 106 maybe doped subsequent to deposition.

[0027] The combined thickness of the top-epitaxial layer 106 and thelayer-of-substrate silicon 102 a may provide useable silicon forcreating one or more elements of microelectromechanical devices. Thethickness of the top-epitaxial layer 106 added to the layer-of-substratesilicon 102 a may vary depending on the type of circuit ormicroelectromechanical device. For instance, the combined thickness ofthe top-epitaxial layer 106 and the layer-of-substrate silicon 102 avaries from CMOS circuitry, in which the overall thickness of the CMOScircuitry typically ranges from about 500 Å to 2000 Å, to bipolarcircuitry, in which the overall thickness of the bipolar circuitry mayrange from 0.3 μm to 10 μm. As overall thicknesses of other devicesvary, the combined thickness of the top-epitaxial layer 106 and thelayer-of-substrate silicon 102 a may likewise vary.

[0028]FIG. 2 is a conceptual drawing illustrating an embodiment of across-section of the substructure of a microelectromechanical device 200at a second processing phase. As illustrated in FIG. 2, themicroelectromechanical device 200 includes a substrate 202, alayer-of-substrate silicon 202 a, a buried-oxide layer 204, atop-epitaxial layer 206, and a thermal-oxide layer 210 formed or “grown”over applicable areas of the top-epitaxial layer 206.

[0029] In a preferred embodiment, the substrate 202 comprises a heavilydoped P-type silicon substrate, and the buried-oxide layer 204 comprisesa buried silicon dioxide (SiO₂) layer. The top-epitaxial layer 206 maybe an N-type top-epitaxial layer. Preferably, the thermal-oxide layer210 is formed as an SiO₂ layer that is “grown” atop the N-typetop-epitaxial layer.

[0030] The microelectromechanical device 200 may also include openings230 a and 230 b that are patterned and etched from the thermal-oxidelayer 210. Openings 230 a and 230 b are created for selectively dopingthe underlying layers, such as the top-epitaxial layer 204 and thelayer-of-substrate silicon 202 a, exposed by the openings 230 a and 230b. These underlying layers may be doped using ion-implantation and/ordiffusion. Although FIG. 2 shows only two openings in the thermal-oxidelayer 210, namely openings 230 a and 230 b, the substructure of themicroelectromechanical device 200 may include additional openings in thethermal-oxide layer 210. Alternatively, the substructure of themicroelectromechanical device 200 may include only one opening in thethermal-oxide layer 210.

[0031] Further included in the substructure of themicroelectromechanical device 200 are a number of first-doped regions,illustrated as first-doped regions 234 a and 234 b. First-doped regions234 a and 234 b may be created by either diffusing or ion implanting theappropriate dopant material into layers of the microelectromechanicaldevice exposed by openings 230 a and 230 b, respectively. In a preferredembodiment, the first-doped regions 234 a and 234 b may be created bydiffusing or by ion-implanting a P-type dopant into an N-typetop-epitaxial layer through openings in a SiO₂ thermal-oxide layer. Themicroelectromechanical device 200 may also include an implant oxidelayer grown over the areas exposed by the openings 230 a and 230 b. Thisimplant oxide is used for protecting the areas exposed by openings 230 aand 230 b during the doping process.

[0032] Although FIG. 2 illustrates only two first-doped regions, namelyfirst-doped regions 234 a and 234 b, the substructure of themicroelectromechanical device 200 may include more than two first-dopedregions. Alternatively, the substructure of the microelectromechanicaldevice 200 may include only one first-doped region. Themicroelectromechanical device may also include other beneficial andsacrificial layers typically used in integrated circuit processing.

[0033]FIG. 3 is a conceptual drawing illustrating an embodiment of across-section of the substructure of a microelectromechanical device 300at a third processing phase. FIG. 3 shows an exemplarymicroelectromechanical device 300, which is similar to themicroelectromechanical device 200 in most respects, except as describedherein. As illustrated in FIG. 3, the microelectromechanical device 300includes a substrate 302, a layer-of-substrate silicon 302 a, aburied-oxide layer 304, a top-epitaxial layer 306, a thermal-oxide layer310, at least one second opening 312, first-doped regions 334 a and 334b, at least one second doped region 338, bond-pad locations 350 a and350 b, and a sensing element 360.

[0034] The thermal-oxide layer 310 of the microelectromechanical device300 is patterned and etched or otherwise removed to create at least onesecond opening 312. Except for locations reserved for runners,connection paths and/or bond pads, such as bond pad locations 350 a and350 b, the second opening 312 exposes all areas of the top-epitaxiallayer 306. Given that the thermal-oxide layer 310 generally provides abarrier that shields underlying layers from being altered duringprocessing, by creating the second opening 312 any of the several of theunderlying layers may be altered with additional processing.

[0035] As such, at least one second-doped region 338 may be created byblanket doping the exposed top-epitaxial layer 306. If, for example, thetop-epitaxial layer 306 is N-type, then preferably, the second-dopedregion 338 is P-type. This P-type region may be created by blanketdoping the N-type top-epitaxial layer using P-type dopants. Blanketdoping also increases the concentration of dopant atoms in thepreviously doped areas of the top-epitaxial layer 306. Thus, blanketdoping an N-type top-epitaxial layer with a sufficient quantity ofP-type dopant causes a previously un-doped or counter-doped area of theN-type top-epitaxial layer to become a P-type doped region. Also,blanket doping the previously P-type doped regions, such as first-dopedregions 334 a and 334 b, with a sufficient quantity of P-type dopantcauses an increase in dopant concentration. To protect the underlyingtop-epitaxial layer from damage during the blanket doping process, themicroelectromechanical device 300 may optionally include an implantoxide grown over the exposed areas of top-epitaxial layer 306.

[0036] As noted above, the microelectromechanical device 300 alsoincludes sensing element 360. Preferably, the sensing element 360 iscomposed of the first-doped regions 334 a and 334 b, and thesecond-doped region 338. The sensing element 360 may provide the sensingcomponent of the preferred microelectromechanical pressure sensor aswell as of other microelectromechanical devices, such as accelerometers,magnetoresistive sensors or gyroscopes. In these devices, it maycomprise conductive elements, capacitive elements, or other sensingcomponents. The sensing element 360 may also comprise diodes andtransistors. Other configurations are possible as well.

[0037] During one of the various phases of processing, certain featuresor components of the microelectromechanical device 300 may be fabricatedfor use in subsequent fabrication phases. Depending on the configurationand type of microelectromechanical device being fabricated, during thefabrication of the device, material from one or more layers may beremoved to provide for access to underlying layers. Access to anunderlying layer in one phase of the processing may be available forsubsequent processing in later phases. Accordingly, themicroelectromechanical device 300 includes at least one via 348, whichprovides access to the substrate 302.

[0038] The via 348 is created by patterning and etching or otherwiseremoving a predetermined volume of material from layers of themicroelectromechanical device 300. Included in the material removed fromthe layers are portions of the top-epitaxial layer 306, the buried-oxidelayer 304, the layer-of-substrate silicon 302 a, and/or any otherbeneficial or sacrificial layer below the thermal-oxide layer 310.

[0039] Like the via 348, during the processing of themicroelectromechanical device 300, other features or components, such ascircuit-contact region 354, may be fabricated in one phase for laterprocessing. Preferably, circuit-contact region 354 is fabricated overthe area of the substrate 302 exposed by via 348. The circuit-contactregion 354 may be fabricated by doping the exposed area of the substrate302. Alternatively, the circuit-contact region 354 may be fabricated bydoping the exposed area of the substrate 302, and then reacting thedoped area with platinum. Preferably, in a heavily P-type doped siliconsubstrate, such as substrate 302, the circuit-contact region 354comprises an N+circuit-contact region.

[0040]FIG. 4 is a conceptual drawing illustrating an embodiment of across-section of the substructure of a microelectromechanical device 400at a fourth processing phase. As illustrated in FIG. 4, themicroelectromechanical device 400 includes a substrate 402, alayer-of-substrate silicon 402 a, a buried-oxide layer 404, atop-epitaxial layer 406, a thermal-oxide layer 410, at least one secondopening 412, first-doped regions 434 a and 434 b, at least onesecond-doped region 438, bond pad locations 450 a and 450 b, and asensing element 460. In addition, the microelectromechanical device 400may include an insulating layer 414 and a conductive-shield layer 416formed over the substrate 402.

[0041] In an exemplary embodiment, the insulating layer 414 is depositeddirectly over the sensing element 460. Preferably, the insulating layer414 may be fabricated from silicon dioxide (SiO₂) using one of thevarious types of CVD deposition noted above. However, the insulatinglayer 414 may be fabricated using other processes that employ otheroxides or insulators. In addition to providing a chemical barrier, theinsulating layer 414 may function as an electrical insulator thatseparates the sensing element 460 from other components. Further, theinsulating layer 414 may provide a mechanical barrier to protect thesensing element 460 from mechanical damage during processing.

[0042] The microelectromechanical device includes a conductive-shieldlayer 416 formed over the sensing element 460. In a multi-level, layeredembodiment, the conductive-shield layer 416, as deposited, may followthe form of the underlying layers including the sensing element 460.Preferably, the conductive-shield layer 416 is formed from a dopedpolysilicon layer. As described in more detail below, theconductive-shield layer 416 may be alternatively comprised of a layer ofmetal or metallic materials.

[0043] The conductive-shield layer 416 formed from doped polysilicon maybe deposited over some or all of the substrate 402 using one or more ofthe various CVD processes noted above. Further, the doping of thedoped-polysilicon layer may occur using Phosphorus Oxychloride (POCl₃)depositon and drive in operations. Alternatively, the doping may occursimultaneously with the deposition. Alternatively, the doping may occurafter deposition of the polysilicon using an ion implantation process.

[0044] Maintaining the modulus of elasticity (Young's Modulus) of theconductive-shield layer 416 at about the same Young's modulus whendoping the layer of polysilicon may prevent a number of undesiredeffects in the output of the microelectromechanical device 400. Includedamong these undesirable effects are mechanical and thermal hystereses.Accordingly, the mechanical elasticity of the conductive-shield layer416 preferably reflects the modulus of elasticity (Young's Modulus) ofthe layers underlying the conductive-shield layer 416, including thesensing element 460. To provide such mechanical elasticity, theconductive-shield layer 416 is preferably formed from a layer ofpolysilicon doped with a 1E+15 atoms/cm² Boron dose. Theconductive-shield layer 416 may be formed from polysilicon that is dopedusing other dopants and dosages as well.

[0045] As noted above, the microelectromechanical device 400 may includea conductive-shield layer 416 comprised of metal or metallic materials,such as Tungsten (W), Chromium (Cr) or Beryllium (Be). In such case, themetal or metallic materials composing the conductive-shield layer 416may be selected so that metal or metallic materials exhibit a Young'sModulus substantially similar to that of the modulus of elasticity(Young's Modulus) of the layers underlying the conductive-shield layer416. Further, hysteresis in the output of the microelectromechanicaldevice 400 may be prevented if the metal or metallic material thatcomposes the conductive-shield layer 416 is maintained within itselastic deformation region.

[0046]FIG. 5 is a conceptual drawing illustrating an embodiment of across-section of the substructure of a microelectromechanical device 500at a fifth processing phase. FIG. 5 shows an exemplarymicroelectromechanical device 500 with integrated conductive shield,which is similar to the microelectromechanical device 400 in mostrespects, except as described herein.

[0047] Referring to FIG. 5, the microelectromechanical device 500includes a substrate 502, a layer-of-substrate silicon 502 a, aburied-oxide layer 504, a top-epitaxial layer 506, a thermal-oxide layer510, at least one second opening 512, an insulating layer 514, aconductive-shield layer 516, first-doped regions 534 a and 534 b, atleast one second-doped region 538, bond pad locations 550 a and 550 b,and a sensing element 560. In addition, the microelectromechanicaldevice 500 includes vias 548, 552 a and 552 b and circuit-contactregions 554, 556 a and 556 b. The microelectromechanical device 500 mayalso include a passivation layer 518, and a first-metal layer 562deposited over at least one part of the passivation layer 518. Themicroelectromechanical device 500 may include several other metal layers(not shown), such as barrier and top-level metalization layers.

[0048] The passivation layer 518 may be fabricated from SiO₂ depositedor grown over at least a portion of the layers deposited over thesubstrate 502. Preferably, the passivation layer 518 is deposited overthe side of substrate 502 containing the layers of material for creatingthe microelectromechanical device 500. While the passivation layer 518may be deposited on the entire side of substrate 502, preferably,predetermined areas of the layers may be masked-off for subsequentprocessing.

[0049] The passivation layer 518 may provide an electromechanicalbarrier against external environments that are impressed upon themicroelectromechanical device 500. In one exemplary embodiment, thepassivation layer 518 may comprise a silicon nitride layer (Si₃N₄). Inaddition to providing an electromechanical barrier against externalenvironments, the Si₃N₄ layer may also provide scratch and moistureprotection. The passivation layer 518 fabricated from un-doped Si₃N₄ mayprovide a sodium barrier, a strong dielectric, and an oxidation barrierfor the elements of the microelectromechanical devices protected by thelayer. The passivation layer 518 may be fabricated using othermaterials, as well.

[0050] Vias 548, 550 a and 550 b provide access to underlying layers ofthe microelectromechanical device 500. Preferably, vias 552 a and 552 bprovide access to the thermal-oxide layer 510. Vias 552 a and 552 b mayalso furnish access to several of the underlying layers for fabricatingother elements, such as bond pads and runner paths. Thus, vias 552 a and552 b may correspond to the bond pad locations 550 a and 550 b,respectively. Although only three vias, namely vias 548, 550 a and 550b, for accessing underlying layers of the microelectromechanical device500 are illustrated in FIG. 5, the microelectromechanical device 500 mayinclude more or less than three vias.

[0051] Included in the microelectromechanical device 500 is a pluralityof substrate circuit-contact regions, such as circuit-contact regions554, 556 a, and 556 b. The circuit-contact regions 554, 556 a and 556 bmay include platinum salicide (PtSi) contacts formed over the areas ofthe substrate 502 that correspond to the areas exposed by vias 548, 550a and 550 b, respectively. The substrate circuit-contact regions mayinclude contacts formed from other metals or conductive materials aswell.

[0052] In one embodiment, circuit-contact region 554 may provide alocation for coupling the conductive-shield layer 516 to the substrate502. The conductive-shield layer 516 may couple or otherwise connect tothe substrate 502 at the circuit-contact region 554 through via 548. Bycoupling the conductive-shield layer 516 to the substrate 502, theconductive shield and the substrate may be placed at substantially thesame voltage. This voltage may be at a constant voltage, oralternatively, at varying potentials. Further, the voltage may be at avoltage less than or greater than ground potential, or at groundpotential of sensing element.

[0053] Alternatively, if the microelectromechanical device 500 is astand-alone microelectromechanical device having a external node forcoupling or otherwise connecting the conductive-shield layer, then theconductive-shield layer 516 may be coupled or otherwise connected withthis node. Once coupled or otherwise connected to the external node, theconductive-shield layer 516 may be placed at the voltage of the externalnode. As another alternative, if the microelectromechanical device 500is part of another system having a node for coupling or otherwiseconnecting the conductive-shield layer, the conductive-shield layer 516may likewise be coupled or otherwise connected with the node of suchsystem. Once coupled or otherwise connected to the node, theconductive-shield layer 516 may be placed at the voltage of the system.

[0054] An exemplary arrangement for coupling the conductive-shield layer516 with the substrate 502 at one of the circuit-contact regions may beprovided by simply depositing anN-type-doped-polysilicon-conductive-shield layer over anN-type-circuit-contact region in a P-type substrate. In anotherexemplary arrangement, the coupling of the conductive-shield layer 516with the substrate 502 at the substrate circuit-contact region 554 maybe provided by the contact created between an N-type doped polysiliconconductive-shield layer deposited over a PtSi contact formed over anN-type circuit-contact region in a P-type substrate.

[0055] In an alternative arrangement, coupling the conductive-shieldlayer 516 with the substrate 502 may be provided by physical contactbetween a polysilicon film or metal film deposited directly over theN-type substrate circuit-contact region. In yet another arrangement, theconductive-shield layer 516 may couple with the substrate 502 throughvia 548. This coupling may be provided by a contact formed fromdepositing a metal or metallic conductive-shield layer and reacting themetal or metallic conductive-shield layer with an N-type substratecircuit-contact region. Other coupling constructions are possible aswell.

[0056] Further, depending on how much the conductive-shield layer 516covers the sensing element 560, coupling the conductive-shield layer 516with the substrate 502 at circuit-contact region 554 may provide forpartial or complete encapsulation of the sensing element 560. In thecase where the conductive-shield layer 516 provides completeencapsulation of the sensing element 560, the conductive-shield layer516 may provide protection of the sensing element 560 from undesired ioninterference. Partial encapsulation of the sensing element 560 may alsoprovide protection against undesired ion interference, notwithstandingthe less than complete encapsulation.

[0057] In the presence of one or more forms of energy, e.g., thermalenergy, ions captured within the microelectromechanical device'scomposition may migrate towards the sensing element 560. In addition,ions from energy rich environments may migrate from the energy richenvironments towards the sensing element 560. Alternatively, ions fromenergy rich environments may cause an exchange of energy in the atoms ofthe microelectromechanical device thereby creating ions within themicroelectromechanical device's composition, which may migrate towardsthe sensing element 560.

[0058] For example, ions from an energy rich environment, such as ionsderived from silicon oil, that are impressed upon the outer surface ofthe passivation layer 518 may migrate, at varying rates, throughpassivation layer 518. Once passing through the passivation layer, theseions may further migrate through voids in the microelectromechanicaldevice's structure. Additionally, the ions from external sources mayionize atoms in the structure of the passivation layer 518, which inturn migrate to the sensing element 560 by exchanging charges amongstthe atoms of the passivation and underlying layers.

[0059] As another example, bathing the microelectromechanical device500, which contains a passivation layer 518 fabricated from Si₃N₄, in asilicon oil bath containing free ions and subjecting the device to asufficient energy source may cause random atoms of the Si₃N₄ passivationlayer 518 to become ionized. With sufficient energy, these charged atomsmay migrate towards the sensing element 560 that, in turn, may cause theoutput of the microelectromechanical device 500 to drift because of thechanging electron or hole conduction.

[0060] In an exemplary embodiment of the microelectromechanical device500 in which the conductive-shield layer 516 covers at least one portionof the sensing element 560, and the conductive-shield layer 516 iscoupled to a voltage source, undesired ions that migrate from externalsources towards the sensing element may be attracted to theconductive-shield layer 516. Similarly, the conductive-shield layer 516may attract the undesired and internally derived ions or charged atoms.To facilitate ion attraction, the conductive-shield layer 516 ispreferably coupled to the substrate 502. Then, the combination is placedat the same voltage, preferably ground potential. Placing thecombination at the same voltage may cause the charged atoms to migratetowards the conductive shield, rather than the sensing element 560.

[0061]FIG. 6 is a conceptual flow diagram 600 illustrating functions forcarrying out the method of fabricating a semiconductormicroelectromechanical device. With reference to FIG. 6, the methodincludes forming a sensing element on a substrate, as shown in block602, forming a conductive-shield layer over the sensing element, asshown in block 604, and coupling the conductive-shield layer to thesubstrate, as shown in block 606.

[0062] As illustrated in FIG. 6, an exemplary embodiment of the methodof fabricating the microelectromechanical device includes the forming asensing element on a substrate, as shown in block 602. The sensingelement may include the sensor used in pressure sensor devices,accelerometer devices, force sensor devices, humidity sensor devices,level sensor devices, magnetosensor devices, and infrared sensordevices, for example. The sensor, in these devices, may comprise oftransistors, diodes, resistors, or capacitors. Forming a sensing elementon a substrate, at block 602, may include implanting oxygen into asilicon substrate to create a buried-oxide layer, which in turn createsa layer-of-substrate silicon resting above the buried-oxide layer.Alternatively, forming a sensing on a substrate may include creating aburied-oxide layer using a BSOI, BESOI, or other similar process. In amicroelectromechanical device, such as a pressure sensor/transducer, theburied-oxide layer may be implanted beneath one surface of the siliconsubstrate at about 2000 Å from the surface.

[0063] Forming a sensing element on a substrate, as shown in block 602,may also include depositing or disposing an intrinsic top-epitaxiallayer over the layer-of-substrate silicon. A top-epitaxial layer havinga thickness of about 9000 Å is preferred. Further, forming a sensingelement on a substrate, at block 602, may include “growing” athermal-oxide layer over the applicable areas of the top-epitaxial layercovered substrate. Preferably, the thermal-oxide layer is grown to athickness of about 13800 Å. At block 602, in the process of forming asensing element, which includes growing and depositing several layers ofsemiconductor material, and etching or otherwise removing the severallayers, a multi-level, layered configuration of themicroelectromechanical device may result.

[0064] Moreover, forming a sensing element on a substrate, as shown inblock 602, may include performing other integrate circuit fabricationprocesses, such as patterning and etching the thermal-oxide layer forleads, connection paths, and bond pads. Forming a sensing element on asubstrate, as shown in block 602, may additionally include implanting ordiffusing selected areas of the deposited and implanted layers with anappropriate N or P type dopant. Preferably, these selected areas areimplanted with a Boron dopant dose of at about 2.4E+14 atoms/cm² atabout 80 KeV.

[0065] The method of fabricating the microelectromechanical device alsoincludes forming a conductive shield over the sensing element, as shownin block 604. In a multilevel, layered microelectromechanical device,the form of the conductive shield may track the form of underlyinglayers. Forming the conductive shield over the sensing element may beperformed by depositing one or more layers of polysilicon by chemicalvapor deposition, such as LPCVD, Ultrahigh Vacuum CVD, and MolecularBean Expitaxy (MBE). In the preferred microelectromechanical pressuresensor, forming one or more layers of polysilicon may be accomplished bydepositing a first and a second layer of polysilicon. Using LPCVD, thefirst layer of polysilicon may be deposited to achieve a thickness ofabout 1500 Å. To facilitate depositing the polysilicon layer, one ormore parameters of LPCVD process, such as temperature, may becontrolled. Preferably, the temperature during deposition is controlledto about 610 degrees Celsius. Like other parameters of the LPCVDprocess, the temperature, however, may be varied.

[0066] Additionally, the second layer of polysilicon, which may comprisemechanical quality or low stress polysilicon, may be deposited by anLPCVD process to achieve a thickness of about 1500 Å. During deposition,the temperature is controlled to at approximately 598 degrees Celsius.As with depositing the first layer of polysilicon, the temperature ofthe LPCVD process when depositing the second layer of polysilicon may bevaried.

[0067] During deposition, the conductive shield may require doping thepolysilicon, which may be provided in-situ by introducing the properconcentration of N or P type atoms. Alternatively, forming theconductive shield over the sensing element, shown at block 604, mayinclude post-deposition doping by way of ion implantation. In thepreferred microelectromechanical-pressure-sensor device, thepost-deposition ion implantation may include implanting a phosphorousdopant dose of about 1E+15 atoms/cm2 at about 50 KeV into the depositedpolysilicon. In another exemplary alternative, the doping of thepolysilicon may be performed using POCl₃ deposition and drive inoperations.

[0068] Forming the conductive shield over the sensing element, shown inblock 604, may also include annealing the layered substrate containingthe doped polysilicon layer. In a microelectromechanical device such asa pressure sensor or accelerometer, forming a conductive shield over thesensing element, shown in block 604, may preferably include apost-deposition anneal at about 950 degrees Celsius in a nitrogen (N₂)environment for a period not less than 250 minutes. Also included informing a conductive shield over the sensing element, at block 604, arethe processing steps for shaping the shield into a specificconfiguration so that at least part of the sensing element is covered.

[0069] In an alternative embodiment, forming the conductive shield overthe sensing element, as shown in 604, may include may include depositinga layer of metal, such as copper, aluminum, titanium-tungsten, gold orother metal or alloy. Metal deposition techniques for depositing theconductive shield over the sensing element may include a CVD process,such as Ultrahigh Vacuum CVD.

[0070] The method of fabricating the microelectromechanical device alsoincludes coupling the conductive shield to the substrate, as illustratedin block 606. The shape of the conductive shield and the structure ofthe microelectromechanical device's layers may affect the method ofcoupling the conductive shield to the substrate. As such, the couplingof the conductive shield to the substrate, at block 606, may vary. Forinstance, the conductive shield may be coupled to the substrate usingcapacitive coupling, resistive coupling, or any other electricalcoupling.

[0071] Coupling the conductive shield to the substrate, as shown inblock 606, may include creating a circuit-contact region in thesubstrate, and connecting the conductive-shield to the circuit-contactregion. In a preferred embodiment, this circuit-contact region may befabricated by ion implanting or diffusing a dopant into the substrate.Alternatively, coupling the conductive shield to the substrate may beaccomplished using a metalization-interconnection system, as describedin more detail below.

[0072]FIG. 7 is a conceptual flow diagram 700 illustrating alternativefunctions for carrying out the method of fabricating amicroelectromechanical device with an integrated conductive shield. FIG.7 shows an exemplary flow diagram 700, which is similar to the flowdiagram 600 in most respects, except as described herein. In a preferredembodiment, the method of fabricating a semiconductormicroelectromechanical may include (i) forming a sensing element on asubstrate 702; (ii) creating one or more circuit-contact regions in thesubstrate, as shown in block 710; (iii) forming a conductive shield, asshown in block 704; (iv) forming an insulating layer between theconductive shield and the sensing element, as shown in block 712; (v)patterning and etching the conductive shield, as shown in block 716;(vi) patterning and etching layers between the conductive shield andsubstrate, as shown in block 718; (vii) forming ametalization-interconnection system, as shown in block 722; (viii)coupling the conductive shield to substrate, as shown in block 706; and(ix) forming a passivation layer over the substrate, as shown in block724.

[0073] Creating one or more circuit-contact regions in the substrate, asshown in block 710, may be performed by ion implanting or diffusing adopant into the substrate in selected areas. The doped areas may then bereacted with one or more metals, such as platinum (Pt) and/or copper.

[0074] At block 712, forming an insulating layer between the conductiveshield and the sensing element may be provided by growing an oxidelayer, such as a SiO₂ thermal-oxide layer, or depositing another type ofinsulator. This insulating layer may function as an electrical insulatorthat separates the sensing element from other layers of themicroelectromechanical device. Further, by forming the insulating layerbetween the conductive shield and sensing element, the insulating layermay protect the sensing element and other layers from mechanical damage.

[0075] The method 700 of fabricating the microelectromechanical devicealso includes forming a conductive shield over the sensing element, asshown in block 704. Forming the conductive shield over the sensingelement, as shown in block 704, may include depositing or disposing aconductive shield layer over at least one portion of the sensing elementor other part of the substrate using a CVD process. In forming theconductive shield layer, a layer of polysilicon may be deposited over aportion of the layered substrate containing the sensing element, andthen the layer of polysilicon may be doped to make it conductive.Alternatively, forming the conductive shield over the sensing element,as shown in block 704, may include depositing a layer of metal, such ascopper, aluminum, titanium-tungsten, gold or other metal or alloy overthe layered substrate containing the sensing element.

[0076] In a preferred embodiment of the fabrication of amicroelectromechanical device, the method 700 may include patterning andetching selective areas of the conductive shield to expose areas of thesubstrate and/or other underlying layers, as shown in block 716.Further, the method 700 of fabricating a microelectromechanical devicemay include pattering and etching selected areas between the conductiveshield and the substrate to expose areas of the substrate and/or otherunderlying layers, as shown in block 718.

[0077] Also included in the method 700 of fabricating amicroelectromechanical device is the process of forming ametalization-interconnection system, as shown in block 722. During theprocess of forming a metalization-interconnection system, the conductiveshield may be coupled or connected to the substrate. Forming ametalization-interconnection system, as shown in block 722, may comprisedepositing a platinum (Pt) layer of about 650 Å over selected areas ofthe substrate by sputtering or other metal deposition process. Further,forming a metalization-interconnection system, as shown in block 722,may include reacting the Pt layer with exposed areas of the substrate tocreate platinum salicide (PtSi) contact areas on the exposed areas ofthe substrate. Moreover, forming a metalization-interconnection system,as shown in block 722, may include removing residual Pt by an etchprocess after creating PtSi contacts.

[0078] Additionally, at block 722, forming ametalization-interconnection system may include depositing one or moremetal layers. These metal layers may be deposited and connected tovarious layers of the microelectromechanical device. Accordingly,forming a metalization-interconnection system may include depositing afirst-level metal, such as titanium-tungsten (TiW), over the exposedareas of the substrate or other underlying layers. The deposition of thefirst-level metal may be accomplished using a sputtering process orother metal deposition technique. Depositing the first-level metal mayprovide an electrical contact, or conductive plug, that connects theconductive shield with the PtSi contact on the substrate.

[0079] Forming a metalization-interconnection system may also includedepositing a second-metal layer, such as gold, using a sputteringprocess or other metal deposition technique. Depending on the thicknessof layers between the conductive shield and the substrate, the thicknessof the multilevel metals varies accordingly. Likewise, depending on thelocation of any layer or layers and the location of the conductiveshield, the depositing of a second-metal layer may provide the couplingbetween the conductive shield and the substrate.

[0080] Also included in an embodiment of the method 700 of fabricating amicroelectromechanical device is the process of coupling the conductiveshield to the substrate, as shown in block 706. Coupling the conductiveshield to the substrate, as shown in block 706, may be accomplished bycoupling and/or connecting the conductive shield layer tocircuit-contact regions located on the substrate. The coupling and/orconnecting the conductive shield layer to the circuit-contact regionsmay be accomplished using a metalization-interconnection system. In analternative embodiment, the process of coupling the conductive shield tothe substrate may include attaching a strap, such as a gold wire,between the conductive shield layer and some external node.

[0081] In accordance with the method 700 of providing amicroelectromechanical device, coupling or connecting the conductiveshield to the substrate may function to preventing ion contamination. Tofacilitate the process of preventing ion contamination of the sensingelement, the combination of the conductive shield and the substrate maybe placed at a specific voltage or potential. In some conditions, thiscombination will be placed at a constant voltage. Alternatively, placingthe combination of the conductive shield and the substrate at a voltagegreater than the largest output of the sensing element may provide thefunction of preventing ion contamination of the sensing element. Othervoltage options are possible. The options that place the conductiveshield at a specific voltage or potential, in effect, cause theconductive shield to attract undesired ions, and function as a Faradayshield.

[0082] The method of fabricating the microelectromechanical device alsoincludes forming a passivation layer over the substrate, as shown inblock 724. Preferably, forming a passivation layer over the substrate,as shown in block 724, is achieved by depositing a layer of siliconnitride Si₃N₄ over the exposed substrate. Alternatively, in the case ofa polysilicon-conductive-shield layer, forming a passivation layer overthe substrate may be achieved by growing a SiO₂ layer over thesubstrate. In the case of a metal conductive shield, forming apassivation layer over the substrate may be accomplished by forming asilicon layer over a metal conductive shield.

[0083] The microelectromechanical device, and method of fabricating thesame, results from the realization that the current configurations ofnon-planar microelectromechanical devices have no conductive layerbetween the device's elements and the exposed top surfaces of thepassivation that stabilizes the microelectromechanical device's output.However, a layer of patterned metal or mechanical-quality, dopedpolysilicon inserted between the appropriate device element layers mayprovide a conductive layer to prevent the microelectromechanicaldevice's output from drifting. The conductive layer may form an almostcomplete encapsulation of the device's elements, or may selectivelycover certain of the device's elements. Further, coupling the metal ormechanical-quality, doped polysilicon to the same voltage source as thedevice's substrate contact may subject the conductive layer to thevoltage of the substrate.

[0084] In view of the wide variety of embodiments to which theprinciples of the present invention can be applied, it should beunderstood that the illustrated embodiments are exemplary only, andshould not be taken as limiting the scope of the present invention. Forexample, the steps of the flow diagrams may be taken in sequences otherthan those described, and more or fewer elements may be used in theblock diagrams. The claims should not be read as limited to thedescribed order or elements unless stated to that effect. In addition,use of the term “means” in any claim is intended to invoke 35 U.S.C.§112, paragraph 6, and any claim without the word “means” is not sointended. Therefore, all embodiments that come within the scope andspirit of the following claims and equivalents thereto are claimed asthe invention.

[0085] Preferred and alternative embodiments of the present inventionhave been illustrated and described. It will be understood, however,that changes and modifications may be made to the invention withoutdeviating from its true spirit and scope, as defined by the followingclaims.

What is claimed is:
 1. A semiconductor microelectromechanical devicecomprising: a substrate; a sensing element formed on the substrate; anda conductive shield formed over the sensing element, wherein theconductive shield is coupled to the substrate.
 2. The semiconductormicroelectromechanical device of claim 1, wherein the conductive shieldcomprises doped silicon.
 3. The semiconductor microelectromechanicaldevice of claim 2, wherein the conductive shield comprises dopedpolysilicon.
 4. The semiconductor microelectromechanical device of claim3, wherein the conductive shield comprises doped, elastic polysilicon.5. The semiconductor microelectromechanical device of claim 1, furtherincluding an insulating layer formed between the sensing element and theconductive shield.
 6. The semiconductor microelectromechanical device ofclaim 5, wherein the insulating layer comprises an oxide film.
 7. Thesemiconductor microelectromechanical device of claim 5, wherein theinsulating layer comprises a silicon dioxide (SiO₂) film.
 8. Thesemiconductor microelectromechanical device of claim 1, furtherincluding a passivation layer formed over the conducting layer.
 9. Thesemiconductor microelectromechanical device of claim 1, wherein theconductive shield coupled to the substrate is placed at substantiallythe same voltage as the substrate.
 10. The semiconductormicroelectromechanical device of claim 1, wherein the conductive shieldand the substrate provide a complete encapsulation of the sensingelement.
 11. The semiconductor microelectromechanical device of claim10, wherein the conductive shield and the substrate are placed atsubstantially the same voltage as the substrate.
 12. The semiconductormicroelectromechanical device of claim 10, wherein the conductive shieldand the substrate are placed at a substantially constant voltage. 13.The semiconductor microelectromechanical device of claim 10, wherein theconductive shield and the substrate are placed at a varying voltage. 14.The semiconductor microelectromechanical device of claim 10, wherein thesubstrate comprises at least one node, the at least one node providing aground voltage, wherein the sensing element formed over the substratehas a ground voltage, wherein the sensing element formed over thesubstrate is coupled to the substrate, and wherein the conductive shieldthat is coupled to the substrate is placed at about the ground voltageof the node of the substrate.
 15. The semiconductormicroelectromechanical device of claim 10, wherein the sensing elementcomprises a first output that provides a first signal in response to anexternal force, semiconductor microelectromechanical device furtherincluding a second output that provides a second signal having a maximumoutput voltage proportional to the first signal, and wherein theconductive shield that is coupled to the substrate is placed at avoltage greater than the maximum output voltage of the second signal. 16The semiconductor microelectromechanical device of claim 1, wherein theconductive shield formed on the substrate provides a partialencapsulation of the sensing element. 17 The semiconductormicroelectromechanical device of claim 16 wherein the conductive shieldand the substrate are placed at substantially the same voltage as thesubstrate. 18 The semiconductor microelectromechanical device of claim16 wherein the conductive shield and the substrate are placed at asubstantially constant voltage. 19 The semiconductormicroelectromechanical device of claim 16 wherein the conductive shieldand the substrate are placed at a varying voltage.
 20. The semiconductormicroelectromechanical device of claim 16, wherein the substratecomprises at least one node, the at least one node providing a groundvoltage, wherein the sensing element formed over the substrate has aground voltage, wherein the sensing element formed over the substrate iscoupled to the substrate, and wherein the conductive shield that iscoupled to the substrate is placed at about the ground voltage of thenode of the substrate.
 21. The semiconductor microelectromechanicaldevice of claim 16, wherein the sensing element comprises a first outputthat provides a first signal in response to an external force,semiconductor microelectromechanical device further including a secondoutput that provides a second signal having a maximum output voltageproportional to the first signal, and wherein the conductive shield thatis coupled to the substrate is placed at a voltage greater than themaximum output voltage of the second signal.
 22. The semiconductormicroelectromechanical device of claim 1, wherein the conductive shieldis doped to a low resistivity.
 23. The semiconductormicroelectromechanical device of claim 1, wherein the substratecomprises a silicon wafer, wherein conductive shield is formed over thesensing element and at least one part of the silicon wafer substrate,and wherein the conductive shield is coupled to the silicon wafersubstrate.
 24. A semiconductor microelectromechanical device comprising:a first-type-dopant substrate; a second-type-dopant epitaxial layer; atleast one sensing element formed in a portion of the second-type-dopantepitaxial layer, an insulating layer formed over at least one portion ofthe at least one sensing element; a conductive-polysilicon layer formedover the at least one portion of the sensing element; a passivationlayer formed over the first-type-dopant substrate; and at least one viaformed between the at least one sensing element and the passivationlayer, wherein the conductive polysilicon layer is coupled to thefirst-type-dopant substrate through the at least one via.
 25. Thesemiconductor microelectromechanical device of claim 24, wherein theconductive-polysilicon layer and the first-type-dopant substrate areplaced at substantially the same voltage.
 26. The semiconductormicroelectromechanical device of claim 24, further including anenclosure, and a strap, wherein the strap couples the first-type-dopantsubstrate and the enclosure.
 27. The semiconductormicroelectromechanical device of claim 26, wherein the enclosure isplaced at a constant potential.
 28. The semiconductormicroelectromechanical device of claim 24, further including: asecond-type-dopant region in the first-type-dopant substrate; and atleast one conductive plug provided in the at least one via coupling theconductive-polysilicon layer and the second-type-dopant region, whereinthe conductive-polysilicon layer and the second-type-dopant region areplaced at substantially the same potential.
 29. A semiconductormicroelectromechanical device comprising: a substrate; a top-epitaxiallayer formed over the substrate; a thermal-oxide layer grown over atleast a portion of the top-epitaxial layer; at least one runnerpatterned and etched in at least a portion of the thermal-oxide layer; asensing element formed in the top-epitaxial layer; and a conductiveshield formed over at least a portion of the sensing element.
 30. Thesemiconductor microelectromechanical device of claim 29, furtherincluding a metalization-interconnection system, wherein themetalization-interconnection system interconnects the conductive-shieldlayer to the substrate.
 31. The device of claim 30, wherein thesemiconductor microelectromechanical device is selected from a groupconsisting of pressure sensors, accelerometers, humidity sensors,automotive sensors, current sensors, fiber optic sensors, force sensors,infrared sensor, mass airflow sensors, photosensors, proximity sensors,level sensors, temperature sensors, turbidity sensors, magnetoresistivesensors, magnetic random access memories or ultrasonic sensors.
 32. Thedevice of claim 30, wherein the semiconductor microelectromechanicaldevice comprises a silicon on insulator pressure sensor.
 33. The methodof claim 32, wherein the top-epitaxial layer is formed to a thickness ofabout 9000 Å.
 34. The device of claim 32, wherein the thermal-oxidelayer is grown to a thickness of about 13800 Å.
 35. The device of claim32, wherein the conductive shield comprises a first-conductive-shieldlayer, and wherein the first-conductive-shield layer is formed to athickness of about 1500 Å at approximately 610 degrees Celsius.
 36. Themethod of claim 35, wherein the conductive shield further comprises asecond-conductive-shield layer, and wherein the second-conductive-shieldlayer is formed to a thickness of about 1500 Å at approximately 598degrees Celsius.
 37. The method for fabricating a semiconductormicroelectromechanical device comprising: forming a sensing element on asubstrate; forming a conductive shield over the sensing element; andcoupling the conductive shield to the substrate.
 38. The method of claim37, further including placing the conductive shield and substrate at asubstantially zero potential difference.
 39. The method of claim 37,further including placing the conductive shield and substrate at asubstantially constant voltage.
 40. The method of claim 37, furtherincluding placing the conductive shield and substrate at a variablevoltage.
 41. The method of claim 37, wherein the sensing elementprovides an output having a maximum voltage signal, and furtherincluding placing the conductive shield layer and substrate at a voltagegreater than the maximum voltage signal.
 42. The method of claim 37,further including: forming at least one conductive plug; and placing theconductive shield and substrate at a substantially zero potentialdifference, wherein the conductive shield couples to the substratethrough the at least one conductive plug.
 43. The method of claim 37,further including: forming at least one conductive plug; and placing theconductive shield and substrate at a substantially constant voltage,wherein the conductive shield couples to the substrate through the atleast one conductive plug.
 44. The method of claim 37, furtherincluding: forming at least one conductive plug; and placing theconductive shield and substrate at a variable voltage, wherein theconductive shield couples to the substrate through the at least oneconductive plug.
 45. The method of claim 37, wherein the semiconductormicroelectromechanical device comprises an output having a maximumvoltage signal, the method further including: forming at least oneconductive plug; and placing the conductive shield and substrate at avoltage greater than the maximum voltage signal of the semiconductormicroelectromechanical device, wherein the conductive shield couples tothe substrate through the at least one conductive plug.
 46. A method forfabricating a semiconductor microelectromechanical device comprising:depositing a top-epitaxial layer over a substrate; growing athermal-oxide layer over at least a portion of the top-epitaxial layer;patterning and etching at least a portion of the thermal-oxide layer forrunners; patterning and etching the thermal-oxide layer for a sensingelement; forming the sensing element over the substrate; forming aconductive shield over at least a portion of the sensing element;patterning and etching the conductive shield; and coupling theconductive shield to the substrate.
 47. The method of claim 46, whereinthe semiconductor microelectromechanical device is selected from a groupconsisting of pressure sensors, accelerometers, humidity sensors,automotive sensors, current sensors, fiber optic sensors, force sensors,infrared sensor, mass airflow sensors, photosensors, proximity sensors,level sensors, temperature sensors, turbidity sensors, magnetoresistivesensors, and magnetic random access memories and ultrasonic sensors. 48.The method of claim 46, wherein the semiconductor microelectromechanicaldevice comprises a silicon on insulator pressure sensor.
 49. The methodof claim 47, wherein the top-epitaxial layer is deposited over at leasta portion of the substrate at a thickness of about 9000 Å.
 50. Themethod of claim 47, wherein the thermal-oxide layer is grown to athickness of about 13800 Å.
 51. The method of claim 47, wherein theconductive shield comprises a first-conductive-shield layer, and whereinthe first-conductive-shield layer is formed to a thickness of about 1500Å at approximately 610 degrees Celsius.
 52. The method of claim 51,wherein the conductive shield further comprises asecond-conductive-shield layer, wherein the second-conductive-shieldlayer is formed to a thickness of about 1500 Å at approximately 598degrees Celsius.